This invention relates to an apparatus and a method for concentrating a solution containing salts. More particularly, the invention relates to an apparatus that may be used at the site of an oil or gas drilling operation and that uses the available energy from drilling operations to concentrate the solution. Other sites where brackish or waste waters are collected and stored, such as in lagoons, would also use this apparatus.
The operations necessary to drill an oil or gas well, and pump the natural product to the surface for processing, almost invariably result in large amounts of brackish waste water. The company running the drilling or storage operations must properly dispose of this waste water with an environmentally safe method as recent studies have shown that sources of potable water for humans are being depleted by declining water tables, by pollution of surface sources or by the salting-up of ground and river waters. As established by the U.S. Public Health Service, water for human consumption should contain no more than 500 parts per million (ppm) of dissolved solids. Seawater contains about 35,000 ppm; brackish water is generally classified as containing 1,000 ppm. Many specialized plants have been built around the world to accomplish the job of sufficiently removing salt from water sources. Although the number of plants built over the last decade to purify salt water has increased dramatically, so has the amount of energy needed to keep these plants operational. Indeed, the cost to build and run any of these plants places them out of reach of most small to medium-sized oil or gas drilling operations which normally must dispose of a large amount of salt water from daily operations. Faced with the high cost of changing brackish water brought up from the ground along with the gas or oil into usable water, many wells simply choose to transport it away by truck. This transportation cost must be added into the total cost of producing the fuel, increasing the final cost to the consuming public.
It is known to use hot gases to remove salts from industrial waste waters. U.S. Pat. No. 4,245,998 to Okouchi et al discloses a method and apparatus wherein hot air is injected downward into a concentrator containing a salt solution thereby enhancing an evaporation efficiency in the concentrator preventing scale deposition in the concentrator and piping system. At a later stage therein, cool air is forced onto a crystalizer to make salt crystals for disposal.
Another invention, described in U.S. Pat. No. 3,882,844 to Ohara et al, discloses a submerged hot gas exchanger that has a combustion gas sparge pipe connected thereto. The hot combustion gases are forced through apertures in the upper surface of the sparge pipe and are violently mixed with a heat exchange liquid surrounding the sparge. The resulting liquid flows past a series of heat-exchanger pipes and transfers heat to a cooler liquid therein.
Although both of these inventions show that it is possible to use hot gases to evaPorate or concentrate liquids, neither uses a dual-method approach as disclosed in the attached specification.